Synthesis and applications of theranostic oligonucleotides carrying multiple fluorine atoms

Self-Assembly and Biological Properties of Highly Fluorinated Oligonucleotide Amphiphiles

Nucleic acids, used as therapeutics to silence disease-related genes, offer significant advantages over small molecule drugs: they provide high specificity, the ability to target "undruggable" molecules, and adaptability to a wide range of disease phenotypes. However, their instability in biological media, as well their rapid clearance from the organism limit their applicability, necessitating the use of nanocarriers to overcome these challenges. Among these strategies, spherical nucleic acids (SNA)-composed of a densely packed corona of oligonucleotides around a nanoparticle-have emerged as a powerful tool, in particular when self-assembled from DNA amphiphiles. This non-covalent strategy however has caveats, especially when it comes to stability in complex biological media, where these SNAs disassemble in contact to serum proteins. Here, we developed highly fluorinated DNA amphiphiles that readily self-assemble into SNAs and have tunable stability profiles in biological media. They are made of branched fluorinated moieties with potentially improved biodegradability as compared to their linear counterparts. Depending on the number of fluorophilic interactions, the self-assembled SNAs can have excellent serum stabilities-up to days-and readily deliver nucleic acid therapeutics for gene silencing applications. These systems show great potential as promising candidates for nucleic acid-based therapies.

First in vivo fluorine-19 magnetic resonance imaging of the multiple sclerosis drug siponimod

Theranostic imaging methods could greatly enhance our understanding of the distribution of CNS-acting drugs in individual patients. Fluorine-19 magnetic resonance imaging (¹⁹F MRI) offers the opportunity to localize and quantify fluorinated drugs non-invasively, without modifications and without the application of ionizing or other harmful radiation. Here we investigated siponimod, a sphingosine 1-phosphate (S₁P) receptor antagonist indicated for secondary progressive multiple sclerosis (SPMS), to determine the feasibility of in vivo ¹⁹F MR imaging of a disease modifying drug. Methods: The ¹⁹F MR properties of siponimod were characterized using spectroscopic techniques. Four MRI methods were investigated to determine which was the most sensitive for ¹⁹F MR imaging of siponimod under biological conditions. We subsequently administered siponimod orally to 6 mice and acquired ¹⁹F MR spectra and images in vivo directly after administration, and in ex vivo tissues. Results: The ¹⁹F transverse relaxation time of siponimod was 381 ms when dissolved in dimethyl sulfoxide, and substantially reduced to 5 ms when combined with serum, and to 20 ms in ex vivo liver tissue. Ultrashort echo time (UTE) imaging was determined to be the most sensitive MRI technique for imaging siponimod in a biological context and was used to map the drug in vivo in the stomach and liver. Ex vivo images in the liver and brain showed an inhomogeneous distribution of siponimod in both organs. In the brain, siponimod accumulated predominantly in the cerebrum but not the cerebellum. No secondary ¹⁹F signals were detected from metabolites. From a translational perspective, we found that acquisitions done on a 3.0 T clinical MR scanner were 2.75 times more sensitive than acquisitions performed on a preclinical 9.4 T MR setup when taking changes in brain size across species into consideration and using equivalent relative spatial resolution. Conclusion: Siponimod can be imaged non-invasively using ¹⁹F UTE MRI in the form administered to MS patients, without modification. This study lays the groundwork for more extensive preclinical and clinical investigations. With the necessary technical development, ¹⁹F MRI has the potential to become a powerful theranostic tool for studying the time-course and distribution of CNS-acting drugs within the brain, especially during pathology.

Versatile Fluorine-Containing Building Blocks: β-CF3-1,3-enynes

The development of diversity-oriented synthesis based on fluorine-containing building blocks has been one of the hot research fields in fluorine chemistry. β-CF₃-1,3-enynes, as one type of fluorine-containing building blocks, have attracted more attention in the last few years due to their distinct reactivity. Numerous value-added trifluoromethylated or non-fluorinated compounds which have biologically relevant structural motifs, such as O-, N-, and S-heterocycles, carboncycles, fused polycycles, and multifunctionalized allenes were synthesized from these fluorine-containing building blocks. This review summarizes the most significant developments in the area of synthesis of organofluorine compounds based on β-CF₃-1,3-enynes, providing a detailed overview of the current state of the art.

Upregulating microRNA‐210 to Inhibit Apoptosis of Neural Stem Cells with an MRI–Visible Nanomedicine for Stroke Therapy

Transplantation of neural stem cells (NSCs) is a promising paradigm for treating stroke. However, the poor survival of transplanted NSCs greatly limits the therapeutic potential. microRNA‐210 (miR‐210), a key hypoxia‐regulated miRNA, can enhance cell survival by targeting the expression of multiple apoptosis‐related genes, such as caspase‐8‐associated protein‐2 (casp8ap2), Bax, and Bcl‐2. Meanwhile, a noninvasive cell‐tracking method is also indispensable for monitoring the in vivo cell‐based therapy. Herein, an MRI–visible nanomedicine is developed to codeliver superparamagnetic iron oxide (SPIO) nanoparticles and miR‐210 into NSCs. This therapeutic nanomedicine not only promotes the survival of NSCs via upregulating miR‐210 to inhibit NSCs apoptosis but also allows an in vivo tracking of transplanted NSCs with MRI. The enhanced NSCs survivability significantly promotes the structural and functional recovery after stroke onset, which highlights the great potential of the multifunctional nanomedicine to improve the therapeutic efficacy of NSCs for stroke treatment.

Strategies for the Synthesis of Fluorinated Nucleosides, Nucleotides and Oligonucleotides

Fluorinated nucleosides and oligonucleotides are of specific interest as probes for studying nucleic acids interaction, structures, biological transformations, and its biomedical applications. Among various modifications of oligonucleotides, fluorination of preformed nucleoside and/or nucleotides have recently gained attention owing to the unique properties of fluorine atoms imparting medicinal properties with respect to the small size, electronegativity, lipophilicity, and ability for stereochemical control. This review deals with synthetic protocols for selective fluorination either at sugar or base moiety in a preformed nucleosides, nucleotides and nucleic acids using specific fluorinating reagents.

Modified Oligonucleotides: New Structures, New Properties, and New Spheres of Application

Nucleic acids have made a long and arduous journey "from the bench to the bedside." At present, it can be assumed that drugs based on modified oligonucleotides will find a worthy application in personalized medicine of the future.